In a refrigerator or refrigerated showcase of the type wherein the substances being refrigerated are placed on holding shelves in the refrigerator or on display racks in the showcase, and a refrigerant gas is made to circulate in direct contact with these substances being refrigerated, low-temperature air obtained from a refrigerating device using a refrigeration cycle, is often used as the refrigerant gas.
In these cases, the low-temperature air has low relative humidity, i.e. it is dry air, since it is obtained by cooling air from outside or by cooling the air in the refrigerator or showcase. Therefore, a phenomenon occurs in which moisture is evaporated from the substances being refrigerated when this dry air is circulated through the refrigerator or showcase.
This phenomenon causes a serious deterioration of the quality of the substances being refrigerated such as cakes, perishable foods, and the like. Even when the refrigeration itself is made satisfactorily, the perishable foods or the like dry out and thereby lose their value as commodities in commerce.